1. Field of the Invention
The present invention relates to a structure of a rotor for a dynamo-electric machine to be mounted to a vehicle and, more specifically, to a structure of a rotor which can resist high velocity revolution and is capable of reducing noise.
2. Description of the Related Art
A dynamo-electric machine to be mounted to a vehicle, more specifically, an alternating-current generator, is increased in velocity by an internal combustion engine. Therefore, it is rotated at a high velocity near the critical limit, and hence various measures against the centrifugal force or against noise are proposed. In JP03-159549A (prior art 1), as a measure against noise, there is disclosed a Lundel-type alternating current generator including a claw-pole type rotor, in which rings (caps) formed of non-magnetic steel are fitted to both ends of a rotor, and the rings are provided with tongue strips for pressing the distal portion of claw-shaped magnetic poles on the opposite side, so that a wind sound generated when being driven at a low velocity and noise generated due to vibrations of the claw-shaped magnetic pole when being driven at a high velocity are reduced.
JP06-077479A (prior art 2) discloses a technology in which rings being formed of non-magnetic steel and having flat portions by the same number as the magnetic poles of the rotor integrally formed by press process are provided on both sides of the rotor, the surfaces of the flat portion that come into abutment with a disk portion of the rotor are welded with the disk portion, and the surfaces of the flat portion that come into abutment with the distal portion of the claw-shaped magnetic poles of the rotor are welded or engaged with the distal portions of the claw-shaped magnetic poles, so that the distal portions of the claw-shaped magnetic poles are fixed to the disk portion of the adjacent rotor, thereby preventing widening of the distal portions of the magnetic poles due to the centrifugal force during high-velocity revolution.
Furthermore, JP07-131946 (prior art 3) discloses a rotor having a first rotor core and a second rotor core having a number of so-called “claw-pole type” claw-shaped magnetic poles, in which a non-magnetic ring for connecting the distal portions of the claw-shaped magnetic poles on one side and the roots of the other claw-shaped magnetic poles on the other side is provided, the claw-shaped magnet poles are formed with grooves for fitting the non-magnetic ring, and the non magnetic ring is welded to the respective claw-shaped magnetic pole, so that the distal portions of the claw-shaped magnetic poles are prevented from being deformed outward due to the centrifugal force generated during high-velocity revolution.
As described above, in the dynamo-electric machine to be mounted to a vehicle, the reason why the non-magnetic ring is mounted to the claw-shaped magnetic poles is to prevent deformation due to the centrifugal force or to reduce vibrations or noise. However, in the technologies in the related art, the claw-shaped magnetic poles that define magnetic path are partially cut off in order to attach the non magnetic ring, which may result in reduction of cross sectional area of the magnetic path or reduction of void area and hence lowering of the performance cannot be avoided.
For example, in the technology disclosed in prior art 1, slight reduction of the cross sectional area of the magnetic path results, and in a state in which the centrifugal force is significant, the distal portions of the claw-shaped poles may come off the ring. Consequently, vibration preventing effect does not work anymore, and hence the effect of noise prevention is deteriorated and, in addition, cooling effect is also deteriorated by using the non-magnet ring or cap, whereby output as the dynamo-rotary machine must be sacrificed. Also, in the technologies disclosed in prior art 2 or prior art 3, reduction of the cross-sectional area of the magnetic circuit or reduction of the void area cannot be avoided. In particular, in the case of prior art 3, if after-treatment after welding is not complete, there is a risk of damaging the end of the coil on a stator side.